As reported to the FAA. Reports are unverified, and codes are left as the FAA publishes them.
What was found
GEG FLIGHT NR 2395: APU WAS RUNNING ABOUT 2 MINUTES. STARTED TO HEAT CABIN RAPIDLY, THEN SMOKEY HAZE FILLED THE CABIN. TURNED OFF APU. MAINTENANCE DEFERRED PER MEL 49-00-1, RSI 352431. MAINTENANCE REMOVED AND REPLACED THE APU IAW MTC 6492001. OPS CHECK GOOD. RAN BLEEDS FULL HOT. NO HAZE NOTED. CLEARS RSI #352431. AIRCRAFT RETURNED TO SERVICE.